As shown in FIG. 1, an existing flat virtual display panel is achieved by disposing two positive lenses 2 in a left-eye display region A and a right-eye display region B in front of a display screen 1 respectively, and a focal distance of each positive lens 2 needs to be larger than a distance from the display screen 1 to the positive lens 2, such that the positive lens 2 acts as a magnifier. A principle of the magnifying function of the positive lens 2 is shown in FIG. 2. In FIG. 2, an image y displayed by the display screen 1 is refracted by the positive lens 2, such that a viewer's eyes may see a magnified positive virtual image y′. The virtual image seen by a left eye and a virtual image seen by a right eye are combined in the viewer's brain so as to generate a stereo visual effect.
In the above described method of achieving the flat virtual display, two positive lenses 2 are needed. However, the positive lenses 2 are thick and heavy, and each positive lens 2 used as a single lens may introduce an optical aberration, which makes the viewer uncomfortable in wearing the virtual display device and in watching a displayed picture, and it is inconvenient for the viewer to watch this virtual display device with his/her eyes being located near to the device.
Therefore, an urgent technical problem to be solved in this technical field is to achieve a flat virtual image display without using any positive lens.